800
FXUS62 KRAH 180001
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
800 PM EDT Tue Sep 17 2024

.SYNOPSIS...
An area of surface low pressure will drift west across
northwestern South Carolina through tonight. The remnants of
this system will linger and gradually dissipate across the mid-
Atlantic through the end of the work week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 245 PM Tuesday...

Regional surface observations and SPC mesoanalysis show the center
of the surface low over upstate SC with a stalled occluded boundary
extending north-northeast towards the Triad and then back east-
southeast through the Triangle and to Goldsboro and off the NC
coast. Along and north of this boundary sufficient easterly low-
level moisture transport some weak instability (500 J/kg of MLCAPE)
are supporting a train of showers and isolated storms. Satellite
imagery confirms low-topped updrafts comprised mostly of water
droplets as well as dry mid-level air spread out across our area
from the stacked low spinning to our west. Steady deepening of
individual clusters has been able to occur over the past couple
hours and will likely continue as instability steadily increases to
around 1000 J/kg. Hi-Res guidance continues to show this regime
slowly spreading northward and elongating along and just south of
the VA/NC border through the evening hours.

The training nature of showers and isolated storms within the
streamer of moisture may result in very narrow swaths of higher
rainfall totals (1-2 inches), most likely over the northern Coastal
Plain into the Northeast Piedmont where instability will be
greatest. Some localized flooding will remain possible, but likely
confined to mostly urban and poor drainage locations along and north
of the boundary.  Some shower activity may continue into the
overnight hours towards the Triad as the occluded low and mid-level
forcing begins to wobble back east.

The stratus layer along and north of the front will gradually lower
through the evening into the overnight hours and may get low enough
to lower surface visibilities to less than 1 mile. Confidence is low
at this time, but may be introduced into the forecast if confidence
in occurrence increases. Overnight lows will settle in the mid 60s
for most locations.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 315 PM Tuesday...

The remnants of PTC 8 and the associated upper low will be over
upstate SC Wednesday morning, with the axis of best deep moisture
shifting north into VA. An occluded front over the Piedmont today
will remain mostly unchanged. The upper trough is forecast to weaken
and open up as it, along with the weak surface reflection, drift
east during the day, with the trough axis likely to be somewhere
over the coastal plain by Thursday morning. Scattered showers will
continue to rotate around the low and will increase in coverage as
some weak instability develops during the day, with the potential
for best coverage near a occluded front/convergence axis that
lingers across the Piedmont.  The best instability is forecast to
spread north from SC into the southern coastal plain during the
afternoon and that is where the depth and coverage of showers or
isolated storms could be best.  The overall deep layer wind field
will be weak and any storms are not expected to be very strong. Deep
moisture is forecast to increase again from the south, as the upper
low/trough begins to slide east, so showers will be heavy, and there
are some indications from the HREF PMM that some showers could
produce up to 2 inches of rain, although they will be isolated and
not likely to cause much of a flooding concern on the whole.

Consistent with the area of better destabilization, the best heating
will be across the south and east as clouds are more likely to
linger in the north and west.  There is good model agreement on
highs ranging from the mid 70s to mid 80s.

The showers will likely continue to the overnight hours in the
vicinity of the upper low and a convergence axis across the northern
portions of the area. Lows will be in the mid to upper 60s with some
decent signals in the SREF for fog north of the boundary as well.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 315 PM Tuesday...

With the exception of Thursday, the majority of the extended
forecast has continued to trend drier. Temperatures will start out
near to slightly above normal, trending slightly below normal late
in the period into early next week. No high-impact weather is
currently anticipated through the period.

On Thursday, we`ll still be under a trough of low pressure aloft,
with its center near New England. The trough axis will bisect the
area, while at the surface, an ill-defined remnant trough is
forecast to be oriented along the I-95 corridor. Isolated to
scattered showers and embedded thunder will be possible in the
aftn/eve, primarily in over the eastern Piedmont, Sandhills, and
Coastal Plain. A secondary area of widely scattered showers may form
over the higher terrain of western NC and impact the Triad. Shear is
lacking so this activity will wane by sunset as instability wanes
and the trough axis shifts east.

From Fri through early next week, the trough near New England and
the Mid-Atlantic is forecast to slowly edge east and off the
Atlantic coast as ridging over the southern Plains and lower MS
valley builds into the Deep South. Weak high pressure will get
replaced by a cool continental surface high from Quebec and
Newfoundland that will nose down into the Mid-Atlantic Sun into
early next week. This will favor pleasant September highs late in
the weekend to early next week of mid to upper 70s to around 80,
about 2-5 degrees below average. Lows will also follow a similar
trend at this time, with some low to mid/upper 50s. Prior to Sun,
we`ll see highs close to seasonal average in the upper 70s to low
80s.

As for rain chances outside of Thu, it looks minimal. Some ensemble
solutions keep the offshore trough closer to the coast, and thus a
few showers could develop inland across the Coastal Plain over the
weekend, but most members are dry. Some solutions also bring
troughing over the OH valley early next week, but keep most of the
energy to our northwest and consequently, dry. We may need to watch
for something later in the week as the operational GFS/CMC and some
EPS/GEFS members show a tropical system coming out of the Caribbean
Sea and into the Gulf. But that`s far enough way and too uncertain
at this point.


&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 800 PM Tuesday...

Anomalous moisture associated with a decaying low pressure system
and sfc front will promote continued sub-VFR conditions over the
next 24 hours.  Residual showers will persist near
KINT/KGSO/KRDU/KRWI the next few hours before waning some overnight.
Ceilings will sock down to IFR/LIFR at these northern terminals over
the next several hours and persist through much of the 24 hour TAF
period. KFAY will also sock down during this period, but may only
reach MVFR restrictions.  The other concern tonight is the potential
for reduced visibilities via fog formation. High-res guidance shows
pretty good chances for fog formation along and north of the front
near KINT/KGSO/KRDU/KRWI. Have added TEMPO groups to account for
this possibility at all terminals. Some clearing has shown over KFAY
this evening. As such, we could see some fog develop there as well.

Sub-VFR ceilings will likely persist through early to mid afternoon
(although KFAY may lift a bit sooner).  Additional scattered showers
and storms may be possible Wednesday afternoon, but overall coverage
should be more limited compared to today.

Outlook: An unsettled period will continue through Thursday with
areas of overnight and early morning stratus and a risk of some
afternoon showers and possibly a storm. Aviation conditions will
generally improve for the weekend.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Blaes
NEAR TERM...Swiggett
SHORT TERM...BLS
LONG TERM...AK
AVIATION...Luchetti/Swiggett